1. Technical Field
The present invention relates to a fuel cutoff valve attached to an upper portion of a fuel tank and configured to open and close a connection conduit for connecting and disconnecting inside of the fuel tank with and from outside.
2. Description of the Related Art
In a fuel cutoff valve designed to discharge the fuel vapor out of a fuel tank, as the fuel is flowed into a valve chest for receiving a float therein in response to a variation of the fuel level during a vehicle drive or in response to a rise of the fuel level during fuel supply, the float lifts up to block the discharge of the fuel vapor. Continued fuel supply in this blockage state increases the internal pressure of the fuel tank and causes blow-off of the fuel. In order to prevent an increase of the internal pressure of the fuel tank and the resulting blow-off of the fuel, one proposed structure of the fuel cutoff valve has small-diameter vent holes formed in a casing including a valve chest as disclosed in, for example, JP-A 2007-92834.
In order to ensure the sufficient liquid tightness and the gas tightness, in attachment of the fuel cutoff valve to a fuel tank, a cover member of the fuel cutoff valve is thermally welded to an upper wall face of the fuel tank. A molten resin used for the thermal welding of the cover member may flow from the position of thermal weld. The vent hole is generally formed in the casing at a position close to the cover member. The molten resin may thus reach the periphery of the vent hole. The small-diameter vent hole pierced through a circumferential wall of the valve chest in the casing may accordingly be blocked by the molten resin. This may interfere with the smooth ventilation of the air in the valve chest.